The present invention relates to a composition which is capable of imparting fluid loss controlling properties to aqueous systems. More particularly, the present invention relates to a composition of a solid particulate material and a cross-linked hydroxyalkyl cellulose, to the formation of a water-based drilling fluid containing the subject composition and to an improved method of drilling bore holes into subterranean formations using said drilling fluid.
In normal well drilling operations in which a well is drilled by a rotary method, the well bore hole is generally filled with a drilling fluid or mud which is circulated therein. Drilling fluids are usually pumped down through the drill stem of the rotary rig, circulated around the drill bit and returned to the surface through the annular passage between the drill stem and the well wall. These drilling fluids perform a number of functions including lubricating the drill stem and bit, cooling the bit, carrying the cuttings from the bit up the bore hole to the surface where the cuttings may be separated and disposed of, and providing a hydrostatic head against the walls of the well to contain downhole geopressure.
A primary requisite of a satisfactory drilling fluid is its ability to inhibit the amount of fluid, normally water, which is lost into the porous strata through which the bore hole traverses. The loss of fluid causes the formation and build-up of a cake deposit which, after a period of time, can cause sticking of the drill pipe and stoppage of the drilling operation. The drilling fluid must, therefore, be of a nature which permits minimum loss into the porous strata. Agents which impart such property are conventionally termed "water loss controllers" or "fluid loss controllers". These terms are used interchangeably in this disclosure.
The drilling fluid must also be capable of exhibiting the above-described fluid loss properties under changing composition and environmental conditions encountered during the drilling operation. The drilling fluid components should be substantially stable to the presence of various calcium compounds and to sodium chloride which may be present in the fluid from the soil strata with which it is in contact and/or due to the use of salt water having calcium or sodium salts therein used in forming the drilling fluid.
It is desired that drilling fluid components be stable and functional at elevated temperature. It is well known that as the bore hole increases in depth the temperatures encountered are substantially above that found at the earth's surface. Further, heat is generated by frictional forces on the drill bit. It is, therefore, desired that components used in forming drilling fluids be stable with respect to varying elevated temperature conditions.
The viscosity imparted to drilling fluids such as by xanthum gums, Wyoming bentonite clay, etc. has been relied upon as a mode of aiding in fluid loss control with little success especially when drilling into and through porous substrates. In attempts to enhance the control properties of such viscosifiers, various agents have been added. For example, in U.S. Pat. No. 3,032,498 a cyanoethylated starch was described as a water loss controller when used in combination with a clay based mud. U.S. Pat. No. 3,988,246 describes an esterfied or etherified starch as a water loss controlling agent which is compatible with a xanthan gum based drilling mud. Other starches have been employed in clay free muds under limiting temperature conditions as starches are known to be temperature sensitive.
There is a general need for a composition which is capable of imparting fluid loss controlling properties to aqueous compositions such as drilling fluid compositions. The composition should be stable to varying conditions and temperatures commonly encountered in drilling operations and must be easily produced at low cost to aid in the economics of drilling operations.